Add Shavian alphabet support (English) (#1924)

This PR adds support for **Shavian**, a phonemic alphabet for English:
https://en.wikipedia.org/wiki/Shavian_alphabet (Unicode
[U+10450–U+1047F](https://www.unicode.org/charts/PDF/U10450.pdf); ISO
15924 - Shaw)
It correctly pronounces most English words, except sometimes it
misplaces the word stress. All checks are passing.
There are many Shavian communities online; I wanted to join in without
excluding people using screen readers.
If needed, this website has more resources: https://shavian.info/
![Screenshot of GNOME terminal, showing the difference between phonemes
in "This is an example sentence in the Shavian alphabet", and the same
sentence but for
Latin](https://github.com/espeak-ng/espeak-ng/assets/113068485/75d43247-1b70-4c16-8e55-6a9ffab7784d)

Continuation of #1818 due to an issue in a rebase